The present invention relates to the storage of files in a file storage system which has a first server including a first file system, and a second server including a second file system.
In recent years, a storage cloud in which files are transferred from a client installed in the respective bases or business divisions to a file server installed in a data center via the internet connection, and controlled centrally in the data center is becoming popular. With this storage cloud, from the perspective of data protection, remote copy of data in the file server is performed. As a system configuration for performing the remote copy of data in the file server, generally adopted is a system configuration including a file server which is accessed by a client during normal operation (hereinafter referred to as the “primary site”), and a file server which is the remote copy destination of the primary site and which is accessed by a client when a failure occurs in the primary site (hereinafter referred to as the “secondary site”). Normally, the primary site and the secondary site are installed at different data centers. In the foregoing system configuration, the secondary site is normally operated in an inaccessible state or in a state which allows Read Only access (hereinafter referred to as the “RO access”). If the secondary site is operated in a state which allows Read/Write access (access which enables Read and Write, and this is hereinafter referred to as the “RW access”), in a low-speed communication environment which connects the client and the data center via internet connection, the client can select the file server of the site having the optimal communication quality as the access destination in consideration of the physical distance to the data center.
As conventional technology related to remote copy between the primary site and the secondary site, disclosed is a configuration of performing asynchronous remote copy from the primary site to the secondary site, managing the difference bit in the primary site, and additionally managing the difference bit in the secondary site (for instance, Japanese Patent Application Publication No. 2009-9333). With the system disclosed in Japanese Patent Application Publication No. 2009-9333, when an access to the secondary site occurs, the difference bit of the primary site and the difference bit of the secondary site are compared to identify the data which has not been sent to the secondary site, the identified data is sent from the primary site to the secondary site, the secondary site is promoted to the primary site, the primary site is changed to the secondary site, and the client thereafter starts its access to the secondary site that was promoted to the primary site. Accordingly, the client can also perform the RW access to the secondary site.